1. Field of the Invention
The present invention relates generally to a method and apparatus for implementing error-control coding in a digital data communications system, and more specifically to such a method and apparatus for correcting and/or detecting errors induced during data transmission.
2. Description of the Prior Art
In order to correct and/or detect channel bit errors induced during digital data transmission, it is well known in the art to utilize error-control coding techniques.
By way of example, these techniques are disclosed in a book entitled "Essential of Error-coding Techniques" edited by Hideki IMAI and published 1990 by Academic Press, Inc., San Diego, Calif. 92101, U.S.A., and a book entitled "Error Control Coding: Fundamentals and Applications" by Shu Lin, et al., published 1983 by Prentice-Hall, Inc., Englewood Cliffs, N.J. 07632, U.S.A.
Redundant bits are added to each binary code word to be transmitted in order to provide the code with the capability of combating channel noise. The Viterbi algorithm is capable of correcting error, almost equally over entire bits of a code word. However, it is sometimes necessary to transmit a special bit(s) of each code word with a high reliability compared with the remaining bits of code word. In order to achieve this result, according to prior art, it has been inevitably required to provide a plurality of pairs of an encoder and decoder having different error-control capability or functions. However, the above mentioned known technique suffers from the drawback that the overall system is rendered large and complex. Further, the freedom of the system design is reduced.